Ozone treating apparatus

ABSTRACT

The present invention provides an ozonization apparatus which is not only capable of dissolving ozone in material water with high efficiency and speedily but also enables the easy and proper control of the dissolved ozone concentration of ozone water. 
     The present invention relates to an ozonization apparatus comprising
         an ozone gas-permeable membrane disposed to isolate material water and ozone gas from each other and allow said ozone gas to be dissolved in said material water by permeation, said ozone gas-permeable membrane being a nonporous hollow tube which is selectively gas-permeable and liquid-impermeable.

TECHNICAL FIELD

The present invention relates to an ozonization apparatus for use in anozone water production system in which ozone gas is dissolved inmaterial water to produce ozone water or a water purification systemutilizing ozone in which ozone is dissolved in a factory effluent orother waste water for an oxidizing treatment, among other applications.

BACKGROUND ART

The ozone water obtained by dissolving ozone gas in water exhibitsexcellent disinfection, deodorization and bleaching actions on accountof the strong oxidizing power of ozone. In addition, because ozone gasundergoes auto-decomposition to oxygen (gas), which is harmless, withthe passage of time and causes no residue problem, it is attractingattention as an ecofriendly disinfectant, cleaner and bleach, forinstance.

In order to insure a positive disinfectant, cleaning and bleachingeffect, the dissolved ozone gas concentration of ozone water must behigh enough but since ozone gas is not only sparingly soluble in waterby nature but has the disadvantage that increasing the ozone gasconcentration frivolously would reduce the efficiency with which ozoneis utilized and, hence, lead to a waste of the material, it is of greatsignificance to control the ozone gas concentration suitably in theproduction and use of ozone water.

The conventional ozone water production and/or purification system whichis generally employed is a bubbling system in which ozone gas is bubbledinto water or an ejector system involving the use of an ejector.

The bubbling system has the disadvantage that it requires a gas-liquidseparation column for removal of bubbles. Moreover, although the finerthe mist of ozone gas bubbled is, the higher is the rate of dissolutionattained, the gas-liquid separation is a time-consuming process. Thus,in the bubbling system, the efficiency of dissolution of ozone gas inwater is very low and the dissolved ozone gas concentration can hardlybe controlled appropriately.

Meanwhile, in the manufacture of semiconductor or liquid crystaldevices, a stripping operation for removing the used photoresist iscarried out frequently in the photolithographic process. In thisphotoresist stripping operation, the use of chemicals in largequantities and the high temperature required for photoresist removalimpose a considerable burden on clean-room air conditioning and amidstthe mounting interest in the protection of environment, a resiststripping technology using ozone water as a substitute for theconventional chemicals is attracting attention.

In connection with the above resist stripping technology involving theuse of ozone water, the relationship of ozone water concentration to theresist striping rate was investigated and it has by now been elucidatedthat increasing the ozone water concentration contributes much to anincreased stripping rate (Collection of Papers Read Before the 8^(th)Annual Research Meeting of Japanese Ozone Association, pp. 14-16, Mar.3, 1998).

Furthermore, although the cleaning of semiconductor wafers and othersubstrates has been conventionally carried out by the RCA process usingsulfuric acid, ammonia or hydrochloric acid, the use of ozone water forthis cleaning has been studied of late from ecological and otherconsiderations (Mitsubishi Electric Technology Vol. 173, Nov. 4, 1999).

Japanese Kokai Publication Hei-7-213880 discloses an ozone gas-permeablemembrane in the form of a porous hollow tube. However, in the case of aporous ozone gas-permeable membrane, it may not be possible to precludecontamination of ozone water with metal particles finding their way intothe ozone gas during gas production insofar as an ozone generator of thesilent discharge type is employed.

SUMMARY OF THE INVENTION

In view of the above state of the art, the present invention has for itsobject to provide an ozonization apparatus which is not only capable ofdissolving ozone in material water with high efficiency and speedily butalso enables the easy and proper control of the dissolved ozoneconcentration of ozone water.

The present invention relates to an ozonization apparatus comprising

an ozone gas-permeable membrane disposed to isolate material water andozone gas from each other and allow said ozone gas to be dissolved insaid material water by permeation, said ozone gas-permeable membranebeing a nonporous hollow tube which is selectively gas-permeable andliquid-impermeable, and said ozone gas-permeable membrane is a membranemade of a fluororesin or a silicone resin. When the ozone gas-permeablemembrane is a membrane made of a fluororesin, it preferably has a tubewall thickness of not more than 0.2 mm, on the other hand, when theozone gas-permeable membrane is a membrane made of a silicone resin, itpreferably has a tube wall thickness of less than 1 mm.

The ozonization apparatus of the present invention preferably comprises

a degassing module for removing dissolved gas from the material water.

The present invention, therefore, is directed to an ozonizationapparatus comprising

a degassing module for removing dissolved gases from the material water,

an ozone dissolution module for dissolving ozone gas in the degassedmaterial water to prepare a primary ozone water, and

an ozone concentration adjusting module for removing a necessary amountof dissolved ozone gas from said primary ozone water to control thedissolved ozone gas concentration and thereby provide a secondary ozonewater. Said ozone concentration adjusting module comprises a negativepressure tank and a degassing tube selectively gas-permeable andliquid-impermeable as installed within said negative pressure tank,

said degassing tube being adapted to admit the primary ozone water whilea reduced pressure is established in the free space within said negativepressure tank or said negative pressure tank being adapted to admit theprimary ozone water while a reduced pressure is established within thelumen of said degassing tube. The degassing tube mentioned above is madeof a fluororesin or a silicone resin.

The ozonization apparatus of the present invention preferably comprises

a first ozone sensor for detecting the dissolved ozone gas concentrationof said primary ozone water and a second ozone sensor for detecting thedissolved ozone gas concentration of said secondary ozone water.

A photoresist stripping apparatus and a substrate cleaning apparatus,both comprising the ozonization apparatus of the invention, are alsopreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elementary view showing one embodiment of the ozonizationapparatus according to the present invention.

FIG. 2 is a schematic view showing an example of the ozone dissolutionmodule to be used in the present invention.

FIG. 3 is an elementary view showing an example of the ozone dissolutionsystem to be used in the present invention.

FIG. 4 is a sketch showing an embodiment of the photoresist strippingapparatus according to the present invention.

FIG. 5 is an elementary view showing an embodiment of the substratecleaning apparatus according to the present invention.

In FIGS. 1 to 5, the reference numeral 1 represents a degassing module,2 an ozone dissolution module, 3 an ozone concentration adjustingmodule, 4 a first ozone sensor, 5 a second ozone sensor, 6 an ozonegenerator, 7 a reservoir tank, 8 an ozone water reservoir tank, 10 amaterial water source (water storage tank), 11 a vacuum tank, 12 adegassing tube, 21 a housing, 22 an ozone gas-permeable membrane, 31 anegative pressure tank, 32 a degassing tube, 41 a photoresist strippingtank, 42 a photoresist-carrying substrate, 43 an etched substratestripped of the photoresist, 53 an ozone compressor, 55 a needle valve,57 a substrate cleaning chamber, 91 a first flowmeter, 93 a secondflowmeter, and 94 an ozone gas sensor. Further, W, W′ each stands formaterial water, OG for ozone gas, OW for primary ozone water, and OW′for secondary ozone water.

DISCLOSURE OF INVENTION

The present invention is now described in detail.

In the following, one embodiment of the ozonization apparatus of theinvention is described in detail, referring to FIG. 1. It should,however, be understood that the present invention is by no means limitedto the specific embodiment illustrated in FIG. 1 but may be implementedin many other forms.

The ozonization apparatus illustrated in FIG. 1 comprises an ozonedissolution module 2 for dissolving ozone gas (OG) in material water(W′) to prepare ozone water (OW) as a nuclear component and, asancillary equipment, further comprises a degassing module 1 whichremoves dissolved gases from material water (W) such as tap water orultrapure water for facilitating dissolution of ozone gas and an ozoneconcentration adjusting module 3 which removes an appropriate amount ofdissolved ozone gas from a primary ozone water (OW) produced by saidozone dissolution module 2 to control the dissolved ozone gasconcentration and thereby produce a secondary ozone water (OW′) which isthe end product. In addition, the apparatus is further equipped with afirst ozone sensor 4 for detecting the concentration of dissolved ozonegas in the primary ozone water (OW) produced by said ozone dissolutionmodule 2 and a second ozone sensor 5 for detecting the concentration ofdissolved ozone gas in the secondary ozone water (OW′) produced by saidozone concentration adjusting module 3.

The degassing module 1 is provided for the purpose of removing dissolvedgases from material water in which ozone gas is to be dissolved tothereby preclude dissolution of unwanted gases other than ozone in ozonewater and facilitate dissolution of ozone gas.

The material water (W) mentioned above is not particularly restrictedbut may for example be tap water, deionized water or ultrapure water.

The degassing module mentioned above is not particularly restricted butmay for example be a device similar to the known vacuum degassingequipment which comprises a vacuum tank 11, a vacuum pump (not shown)for evacuating said vacuum tank 11, and a degassing tube 12 providingfor passage of material water (W) as installed in said vacuum tank 11.

The degassing tube 12 for use in the degassing module 1 is notparticularly restricted provided that it is selectively gas-permeableand liquid-impermeable, thus including a hollow tubular structure madeof, for example, a fluororesin or a silicone resin and having anecessary size in inside diameter and length. The degassing tube 12 isinstalled internally of the vacuum tank 11, with one open end serving asa liquid inlet being communicably connected to a source of materialwater (W) (a water reservoir tank 10), while the other open end servingas a liquid outlet is communicably connected to the ozone dissolutionmodule 2, so that as the material water (W) is admitted from said liquidinlet and caused to flow through the degassing tube 12 while a negativepressure control is maintained in the vacuum tank 11 by a vacuum pump orthe like, the material water (W) is deprived of dissolved gases in thecourse of flow to said liquid outlet.

FIG. 2 shows the ozone dissolution module 2 on exaggerated scale.

The ozone dissolution module 2 is designed to dissolve ozone gas inmaterial water to produce ozone water. More particularly, the module 2is designed to dissolve ozone gas (OG) in material water (W′), viz. thematerial water which has been deprived of dissolved gases in advance, toproduce a primary ozone water (OW). The ozone dissolution module 2comprises a housing 21 and an ozone gas-permeable membrane 22 disposedin said housing 21 to isolate the material water (W′) deprived ofdissolved gases in advance from the ozone gas (OG) supplied from anozone generator 6.

The ozone gas-permeable membrane 22 is made of a membrane material whichis selectively gas-permeable and liquid-impermeable, particularly amembrane material which resists corrosion and aging due to ozone gas andis selectively permeable to ozone gas, such as a fluororesin or asilicone resin.

The fluororesin mentioned above includes tetrafluoroethylene resinpolymers such as polytetrafluoroethylene resin(PTFE), perfluoroalkoxyresin (PFA), fluorimated ethylene-propylene copolymer resin (FEP), andfluorine-containing rubber, among others. As to the silicone resin,methylsilicone rubber can be mentioned, for instance.

The ozone gas-permeable membrane 22 can be produced by molding such amembrane material as above into a nonporous hollow tubular structurehaving a necessary size in inside diameter and length, and a pluralityof unit lengths of such ozone gas-permeable membrane 22 are thermallyfused or bonded end-to-end into a bundle and installed in the housing21.

When a porous membrane is used as said ozone gas-permeable membrane 22,it is difficult to completely prevent contamination of ozone water withmetallic impurities scattered into the ozone gas generated by an ozonegenerator of the silent discharge type but this contamination can becompletely precluded by using a nonporous membrane. Moreover, when ahollow tubular membrane is used as the ozone gas-permeable membrane 22,a large surface area can be provided as compared with the use of amembrane in a sheet form and assuming that the capacity of the ozonedissolution module is constant, a more efficient treatment can becarried out.

When the ozone gas-permeable membrane 22 is made of a fluororesin, thewall thickness of the tube is preferably not more than 0.2 mm, while, inthe case of a membrane made of a silicone resin, the wall thickness ofthe tube is preferably less than 1 mm. If the thickness exceeds theabove limit in either case, a practically acceptable ozone concentrationmay hardly be obtained.

The geometry of the housing 21 is not particularly restricted but may beshaped like a tank or a hollow tubular structure having a necessarylength, for instance. The material of which the housing 21 is made isnot particularly restricted provided that it is highly resistant toozone and gas-tight. As an example, stainless steel can be mentioned.

The ozone gas-permeable membrane 22 is installed in the housing 21 insuch a manner that although the material water (W′) supplied from thedegassing module 1 is isolated from the ozone gas (OG) supplied from theozone generator 6, the ozone gas may come into contact with the materialwater (W′) across the ozone gas-permeable membrane 22 by permeation. Inthis connection, the ozone gas (OG) supply line is preferablypressurized so that the ozone gas (OG) may be forced to permeate throughthe ozone gas-permeable membrane 22. By pressurizing the ozone gas inthis manner, the ozone gas can be dissolved in the material water in alarger quantity and more efficiently.

In order that ozone gas may be dissolved in material water (W′) in theozone dissolution module 2, a hollow tubular ozone gas-permeablemembrane 22 is installed in the housing 21 and the material water (W′)is caused to fill up or flow within the lumen of said ozonegas-permeable membrane 22 while ozone gas (OG) is caused to fill up orflow down the free space within the housing 21 or, conversely, thematerial water (W′) is caused to fill up or flow down the free spacewithin the housing 21 while ozone gas (OG) is caused to fill up or flowdown the lumen of the hollow tubular ozone gas-permeable membrane 22.

In the embodiment illustrated in FIGS. 1 and 2, an ozone gas-permeablemembrane 22 is installed in a generally cylindrical housing 21 in such amanner that one open end of said membrane 22 is disposed at a liquidinlet 21 a of housing 21 while the other open end is disposed at aliquid outlet 21 b of housing 21 to constitute an ozone dissolutionmodule, said liquid inlet 21 a of housing 21 being communicablyconnected to the degassing module 1 to serve as an inlet for materialwater (W′) and said liquid outlet 21 b of housing 21 being connected tothe ozone concentration adjusting module 3 or the reservoir tank 7 toserve as an outlet for primary ozone water (OW).

The ozone generator 6 is communicating with the housing 21 through thegas inlet 21 c formed on the opposite side of the liquid inlet 21 a ofhousing 21 and the internal free space of the housing 21 is maintainedin a pressurized condition by the ozone gas (OG) supplied from the ozonegenerator 6. With the free space within the housing 21 being thuspressurized, the material water (W′) which has been degassed in thedegassing module 1 is admitted from the liquid inlet 21 a into the lumenof the hollow tubular ozone gas-permeable membrane 22 in acountercurrent manner with respect to the flow of ozone gas (OG),whereby the pressurized ozone gas (OG) in the housing 21 is forced topermeate through the hollow tubular ozone gas-permeable membrane 22 anddissolves in the material water (W′), and the resulting primary ozonewater (OW) emerges from the liquid outlet 21 b of the housing 21, whilethe excess ozone gas (OG) is exhausted from a gas outlet 21 d of thehousing 21.

Contrary to the arrangement illustrated in FIGS. 1 and 2, it may be soarranged that ozone gas (OG) is admitted into the lumen of said hollowtubular ozone gas-permeable membrane 22 via said liquid inlet 21 a ofhousing 21 while the material water (W′) is admitted from said gas inlet21 c of housing 21 so that the ozone gas (OG) permeating through theozone gas-permeable membrane 22 is dissolved in the material water (W′).

The ozone generator 6 is not particularly restricted but may for examplebe a silent discharge type in which air or oxygen gas is passed througha silent discharge to generate ozone gas or an ultraviolet irradiationdevice.

The dissolved ozone gas concentration of the primary water (OW) producedby said ozone dissolution module 2 is monitored by the first ozonesensor 4 connected to the ozone dissolution module 2. Since generallythe dissolved ozone gas concentration of the primary water (OW) producedin the ozone dissolution module 2 is fairly high, it may be a prudentchoice to provisionally store the primary ozone water in a reservoirtank 7 (which may serve as a photoresist stripping water tank 41 aswell) and adjust its dissolved ozone gas concentration appropriately inthe ozone concentration adjusting module 3.

The ozone concentration adjusting module 3 removes an appropriate amountof dissolved ozone gas from the primary ozone water (OW) prepared in theozone dissolution module 2 to thereby adjust the dissolved ozone gasconcentration of the end product secondary ozone water (OW′).

The ozone concentration adjusting module 3 is not particularlyrestricted but may for example be a unit comprising a negative pressuretank 31, a vacuum pump (not shown) for decompressing the free spacewithin the negative pressure tank 31, and a degassing tube 32 installedin said negative pressure tank 31.

By admitting the primary ozone water (OW) from the ozone dissolutionmodule 2 into the lumen of said degassing tube 32 while the free spacewithin the negative pressure tank 31 of the ozone concentrationadjusting module 3 or admitting the primary ozone water (OW) from theozone dissolution module 2 into the negative pressure tank 31 while thelumen of the degassing tube 32 is maintained under reduced pressure, anappropriate amount of dissolved ozone gas is removed from the primaryozone water (OW) produced in the ozone dissolution module 2 to adjustthe dissolved ozone gas concentration and thereby provide a secondaryozone water (OW′) of the desired ozone gas concentration.

The degassing tube 32 for use in the ozone concentration adjustingmodule 3 is a tube made of a membrane material which is selectivelygas-permeable and liquid-impermeable, preferably a membrane materialhighly resistant to corrosion and aging due to ozone gas, such as afluororesin or a silicone resin.

As said fluororesin and silicone resin, the same resins as thosementioned for said ozone gas-permeable membrane can be employed.

The degassing tube for use in the invention can be obtained by moldingsuch a membrane material as above into a hollow tubular structure havingthe necessary size in inside diameter and length.

In the embodiment illustrated in FIG. 1, the degassing tube 32 isinstalled within the negative pressure tank 31 with one of its open endsserving as a liquid inlet being connected to the ozone dissolutionmodule 2 for admitting primary ozone water (OW) and the other open endserving as a liquid outlet being connected to an ozone water reservoirtank 8, and the primary ozone water (OW) prepared in the ozonedissolution module 2 is admitted from said liquid inlet into thedegassing tube 32 while the free space within the negative pressure tank31 is maintained under reduced pressure by a vacuum pump or the like,whereby an appropriate amount of dissolved gas is removed from theprimary ozone water (OW) to adjust the dissolved ozone gas concentrationand thereby give a secondary ozone water (OW′) of the desired ozone gasconcentration.

The dissolved ozone gas concentration of the secondary ozone water (OW′)prepared in the ozone concentration adjusting module 3 is monitored by asecond ozone sensor 5 connected to said module 3. However, a singlesensor may be caused to double as said first ozone sensor 4 formonitoring the dissolved ozone gas concentration of the primary ozonewater (OW) from the ozone dissolution module 2 and the second ozonesensor 5 mentioned just above by providing a switch valve (not shown) orthe like device adapted to choose from the alternatives, namelymonitoring of the dissolved ozone gas concentration of primary ozoneconcentration of primary ozone water (OW) or that of the dissolved ozonegas concentration of secondary ozone water (OW′).

The ozone sensors 4 and 5 mentioned above are not particularlyrestricted but each may for example be a continuous-measuringdissolved-ozone monitor utilizing ultraviolet absorption spectrometry.

With the ozonization apparatus of the present invention, ozone water ofthe desired ozone concentration can be produced with safety, ease andhigh efficiency and, therefore, the apparatus can be used in the ozonetreatment of plant effluents or for disinfection, cleaning and bleachingin various industries.

Furthermore, with the ozonization apparatus of the invention, an ozonewater of high concentration can be produced quickly and accurately sothat for the photolithographic process in the manufacture ofsemiconductor or liquid crystal devices, the ozonization apparatus ofthe invention can be utilized to implement a compact photoresiststripping apparatus which is capable of removing the used photoresistwith high efficiency and does not require a bubbling system or agas-liquid separation column. The photoresist stripping apparatuscomprising the ozonization apparatus of the invention is also anembodiment of the present invention.

A specific embodiment of said photoresist stripping apparatus isillustrated in FIG. 4. In the embodiment shown in FIG. 4, the ozonewater produced in the ozone dissolution module 2 is transferred to aphotoresist stripping tank 41 and stored therein. As aphotoresist-carrying substrate 42 is dipped in this high-concentrationozone water pooled in the photoresist stripping tank 41, the photoresistlayer only is selectively removed and the etched substrate 43 can betaken out. The ozone water in the photoresist stripping tank 41 isreturned to the ozone dissolution module 2 so that it may regain apredetermined concentration and be recirculated.

The substrate constituting said photoresist-carrying substrate is notparticularly restricted but, in the manufacture of semiconductordevices, for instance, means a silicon wafer or, in the manufacture ofliquid crystal display devices, means a glass panel. Referring, further,to the photoresist stripping apparatus, means for removing thephotoresist layer with ozone water is not restricted to a circulationtype apparatus comprising a batch unit such as the photoresist strippingbath shown in FIG. 4 but may be a contact type apparatus utilizing aspray system or a curtain flow system, for instance.

Furthermore, since the ozonization apparatus of the invention providesfor the production of a clean ozone water of high concentration withoutrisks for contamination with metal particles originating from an ozonegenerator, the apparatus can be utilized to implement a substratecleaning apparatus. The substrate cleaning apparatus comprising theozonization apparatus of the invention also constitutes an embodiment ofthe invention.

As used in this description, the term “cleaning” means the removal ofsurface dirt and oily contaminants from substrates or the removal of theused photoresist, among others, from substrates in the manufacture ofcircuit boards and the like.

FIG. 5 shows a specific embodiment of said substrate cleaning apparatus.

The embodiment illustrated in FIG. 5 comprises said ozone dissolutionmodule 2 as a nuclear component and further comprises an ozone gassensor 94 for detecting the ozone gas (OG) generated by the ozonegenerator 6, a compressor 53 for pressurizing the ozone gas, a needlevalve 55 which adjusts the degree of evacuation, an ozone sensor 4 fordetecting the concentration of the ozone water (OW) prepared in saidozone dissolution module 2, and a substrate cleaning chamber 57 forcleaning substrates or the like with the product ozone water.

The mode of cleaning within said substrate cleaning chamber 57 is notparticularly restricted but may for example be a dip mode or a spraymode.

The compressor 53 is not particularly restricted provided that it iscapable of pressurizing the ozone gas (OG) produced by the ozonegenerator 6 to the level higher than atmospheric pressure but preferablyis a pressure pump made of ozone-resisting material.

BEST MODE FOR CARRYING OUT THE INVENTION

The following examples illustrate the present invention in furtherdetail without defining the scope of the invention.

REFERENCE EXAMPLE 1 Ozonization Apparatus

As an embodiment of the invention, the ozonization apparatus illustratedin FIG. 3 was constructed.

As the material water (W), tap water adjusted to the same temperature asroom temperature was used and, by means of a pump (manufactured byEYELA, RP-1000), not shown, was fed into the lumen of a hollow tubularozone gas-permeable membrane 22 of the ozone dissolution module 2 via afirst flowmeter 91. On the other hand, as the raw material ozone gas(OG), air was supplied at a pressure of 0.05 MPa via a second flowmeter93. This air was ozonized in an ozone generator 6 (manufactured bySumitomo Precision Industry, SG-C1-PSA2) and, after monitoring of theconcentration of ozone gas by an ozone gas sensor (manufactured by RikoKagaku, OZR 911) 94, the gas was admitted into the ozone dissolutionmodule 2 (the free space within the housing 21) and caused to permeatethrough the hollow tubular ozone gas-permeable membrane 22 and dissolvein material water (W). The dissolved ozone gas concentration of theproduct ozone water (OW) was detected by the ozone sensor (manufacturedby Riko Kagaku, OZR911) 4.

EXAMPLE 1

The ozone dissolution module 2 shown in FIG. 2 and the ozonizationapparatus shown in FIG. 3 were used. As the nonporous hollow tubularozone gas-permeable membrane 22, a bundle of 500 polytetrafluoroethyleneresin (PTFE) tubes each measuring 0.5 mm in inside diameter, 0.15 mmthick, and 1 m long, which meets the AWG (American Wire Gagespecification) 24, was used. The bundle of tubes was set in the housing21, made of poly(vinyl chloride), 30 mm inside diameter and 1,000 mmlong, and while the tap water adjusted to the same temperature as roomtemperature (20° C.) in advance was admitted into the lumen of saidnonporous hollow tubular ozone gas-permeable membrane 22 from the liquidinlet 21 a of the ozone dissolution module 2, an ozone gas of 40 mg/NLconcentration was supplied from the gas inlet 21 c of the ozonedissolution module 2 at a pressure of 0.05 MPa in a countercurrentfashion with respect to the flow of said tap water. In the meantime, theflow rate of the tap water was varied stepwise and the dissolved ozonegas concentration of the ozone water produced was monitored with theozone concentration sensor (manufactured by Riko Kagaku Kenkyusho,OZR911). The results are presented in Table 1.

TABLE 1 Concentration of Flow rate (mL/min) ozone water (mg/L)  50 3.8100 2.4 220 1.2 500 0.8

It is apparent from Table 1 that ozone concentrations not less than 1ppm, which are generally used, could be obtained in Example 1.

EXAMPLE 2

Except that a bundle of 60 PTFE tubes each measuring 0.5 mm in insidediameter, 0.05 mm thick, and 1 m long was used, the ozone concentrationwas measured in the same manner as in Example 1. The results arepresented in Table 2.

TABLE 2 Concentration of Flow rate (mL/min) ozone water (mg/L)  56 3.4112 1.9 220 1.0 360 0.5

It is apparent from the above results that by reducing the membranethickness from 0.15 mm to 0.05 mm, an ozone concentration of the sameorder can be obtained with about one-tenth of the number of tubes,indicating that the efficiency of dissolution of ozone gas is dependenton tube thickness.

REFERENCE EXAMPLE 2

Except that a bundle of 500 PTFE tubes each measuring 0.5 mm in insidediameter, 0.22 mm thick, and 1 m long was used, the ozone concentrationwas measured in the same manner as in Example 1. The results arepresented in Table 3.

TABLE 3 Concentration of Flow rate (mL/min) ozone water (mg/L)  50 0.6110 0.3 220 0.2

It is apparent from the above results that when the tube thicknessexceeds 0.2 mm, a practically useful ozone concentration can hardly beobtained.

EXAMPLE 3

Except that a bundle of 100 silicone tubes each measuring 0.5 mm ininside diameter, 0.25 mm thick, and 1 m long was used as the nonporoushollow tubular ozone gas-permeable membrane, the ozone concentration wasmeasured in the same manner as in Example 1. The results are presentedin Table 4.

TABLE 4 Concentration of Flow rate (mL/min) ozone water (mg/L) 150 7.1250 5.1 330 4.6 550 3.1

It is apparent from the above results that an ozone water of highconcentration could be obtained.

EXAMPLE 4

Except that a bundle of 30 silicone tubes each measuring 1 mm in insidediameter, 0.5 mm thick, and 1 m long was used, the ozone concentrationwas measured in the same manner as in Example 3. The results arepresented in Table 5.

TABLE 5 Concentration of Flow rate (mL/min) ozone water (mg/L) 150 1.6250 1.1 330 1.0 550 0.7

It is apparent from the above results that an ozone water of highconcentration could be obtained.

REFERENCE EXAMPLE 3

Except that a bundle of 15 silicone tubes each measuring 1 mm in insidediameter, 1 mm thick, and 1 m long was used, the ozone concentration wasmeasured in the same manner as in Example 3. The results are presentedin Table 6.

TABLE 6 Concentration of Flow rate (mL/min) ozone water (mg/L) 150 0.5250 0.4 330 0.3 550 0.2

It is apparent from the above results that when the membrane thicknessexceeds 1 mm, a practically useful ozone concentration can hardly beobtained and the dissolution efficiency per unit capacity is lowered toa practically unfavorable level.

EXAMPLE 5 Photoresist Stripping Operation

Using a spin coater (1H-DXNII, manufactured by Mikasa), apositive-acting resist for TFT use (OFPR-PR13, product of Tokyo OhyoKagaku Kogyo) was uniformly applied onto a square glass panel measuring1000×1000 mm and dried by heating at 90° C. for 30 minutes to constructa photoresist layer on the glass substrate. The thickness of the abovephotoresist layer was 1.1 μm.

The above sample was dipped in ozone water in a photoresist strippingtank filled with the ozone water prepared in each of Examples 1 and 2and Reference Example 2 for 30 minutes to investigate the degree ofremoval of the photoresist layer. As a result, whereas the photoresistlayer had been completely removed with the ozone water obtained inExample 1 or 2, only a 0.3 μm portion had been removed with the ozonewater prepared in Reference Example 2.

EXAMPLE 6

Ozone water was prepared using the ozone dissolution module shown inFIG. 2 and the substrate cleaning apparatus utilizing the module asshown in FIG. 5. A bundle of 90 silicone tubes each measuring 0.5 mm ininside diameter, 0.25 mm thick, and 1 m long was set as the nonporoushollow tubular ozone gas-permeable membrane and using a peristaltic pump(manufactured by EYELA, RP-1000), deionized water adjusted to the sametemperature as room temperature in advance was supplied into the lumenof the tube from the inlet (21 a) of the ozone dissolution module at adelivery rate of 260 mL/min.

On the other hand, the ozone gas from the ozone generator (manufacturedby Sumitomo Precision Industry, SG-01-PSA2) was monitored for its gaspressure by an ozone gas concentration sensor (manufactured by EbaraJitsugyo, EG-500) and supplied at a flow rate of 1.3 L/min. This ozonegas was pressurized with a compressor (manufactured by IWAKI, BA-230TN),adjusted to the proper pressure with a needle valve, and fed to a sideinlet (21 c) of the ozone dissolution module, whereby the ozone gas wascaused to permeate across said nonporous ozone gas-permeable membraneand dissolve in the water within the tube lumen.

The concentrations of the ozone water obtained by changing the ozone gaspressure (gauge pressure) stepwise as above are shown in Table 7.

Evaluation of Dirtiness of Semiconductor Wafers

The ozone water having a varying ozone concentration was sprayed against6-inch silicon wafers within the wafer chamber and the contaminationlevel at the semiconductor wafer cleaning stage was evaluated by thequalitative and quantitative analysis of metal foulants remaining on thewafers by inductively coupled plasma mass spectrometry (ICP-MS). Theresults are presented in Table 7.

TABLE 7 Semiconductor wafer Ozone gas Concentration contaminationevaluation pressure of ozone water (metallic contamination (MPa) (mg/L)level) 0.01 2.7 Not more than 10¹¹ atoms/cm² 0.067 4.3 Not more than10¹¹ atoms/cm² 0.15 6.6 Not more than 10¹¹ atoms/cm²

It is apparent from the above results that the concentration of ozonewater was as low as 2.7 mg/L when the pressure (0.01 MPa) from the ozonegenerator was directly used but when the ozone gas pressure was boostedby the pump, the concentration of the product ozone water rose inproportion to the ozone gas pressure as shown in Table 7. Moreover, theevaluation of dirtiness of semiconductor wafers revealed that the metalcontaminant levels at the various ozone water concentrations were notmore than 10¹⁰ atoms/cm², thus being substantially equal to thecontamination level of the unused silicon wafer (blank).

COMPARATIVE EXAMPLE 1

The ozone gas produced by the ozone generator was not passed through theozone dissolution module but was directly dissolved in material waterand the resulting ozone water was used in the same metal contaminationevaluation as in Example 6. As a result, the contamination level wasobviously higher, viz. 10¹¹˜10¹³ atoms/cm².

Thus, unlike the ozone water prepared by contacting the ozone gas fromthe ozone generator directly with water, the ozone water obtained bycausing the ozone gas to permeate across a nonporous tubular ozonegas-permeable membrane and dissolve in material water in the presentinvention is completely free from contaminants originating from theozone gas generator and it has been confirmed that this ozone water isquite suitable for the semiconductor wafer cleaning with ozone water.

Industrial Applicability

The present invention, constituted as above, provides an ozonizationapparatus of simple mechanism and construction, which is not onlyresistant to corrosion and aging due to ozone gas but capable ofdissolving ozone gas selectively in material water to produce ozonewater of a desired concentration with safety, ease, and high efficiency.

1. An ozonization apparatus comprising an ozone gas-permeable membranedisposed to isolate material water and ozone gas from each other andallow said ozone gas to be dissolved in said material water bypermeation, said ozone gas-permeable membrane being a nonporous hollowtube which is selectively gas-permeable and liquid-impermeable, whereinthe ozone gas-permeable membrane is a membrane consisting of atetrafluoroethylene resin polymer or a fluorine-containing rubber, andhas a tube wall thickness of not more than 0.2 mm.
 2. The ozonizationapparatus according to claim 1, wherein the ozone gas-permeable membraneis a membrane consisting of a polytetrafluoroethylene resin, aperfluoroalkoxy resin or fluorimated ethylene-propylene copolymer resin.3. A photoresist stripping apparatus comprising the ozonizationapparatus according to claim
 2. 4. A substrate cleaning apparatuscomprising the ozonization apparatus according to claim
 2. 5. Theozonization apparatus according to claim 1 comprising a degassing modulefor removing dissolved gas from the material water.
 6. A photoresiststripping apparatus comprising the ozonization apparatus according toclaim
 1. 7. A substrate cleaning apparatus comprising the ozonizationapparatus according to claim
 1. 8. An ozonization apparatus comprisingan ozone gas-permeable membrane disposed to isolate material water andozone gas from each other and allow said ozone gas to be dissolved insaid material water by permeation, said ozone gas-permeable membranebeing a nonporous hollow tube which is selectively gas-permeable andliquid-impermeable, wherein the ozone gas-permeable membrane is amembrane consisting of a silicone resin and has a tube wall thickness ofless than 1 mm.
 9. A photoresist stripping apparatus comprising theozonization apparatus according to claim
 8. 10. A substrate cleaningapparatus comprising the ozonization apparatus according to claim
 8. 11.An ozonization apparatus comprising a degassing module for removingdissolved gases from the material water, an ozone dissolution module fordissolving ozone gas in the degassed material water to prepare a primaryozone water, and an ozone concentration adjusting module for removing anecessary amount of dissolved ozone gas from said primary ozone water tocontrol the dissolved ozone gas concentration and thereby provide asecondary ozone water.
 12. The ozonization apparatus according to claim11 comprising a first ozone sensor for detecting the dissolved ozone gasconcentration of said primary ozone water and a second ozone sensor fordetecting the dissolved ozone gas concentration of said secondary ozonewater.
 13. The ozonization apparatus according to claim 11, wherein saidozone concentration adjusting module comprises a negative pressure tankand a degassing tube selectively gas-permeable and liquid-impermeable asinstalled within said negative pressure tank, said degassing tube beingadapted to admit the primary ozone water while a reduced pressure isestablished in the free space within said negative pressure tank. 14.The ozonization apparatus according to claim 13, wherein the degassingtube is made of a fluororesin or a silicone resin.
 15. The ozonizationapparatus according to claim 11, wherein the ozone concentrationadjusting module comprises a negative pressure tank and a degassing tubeselectively gas-permeable and liquid-impermeable as installed withinsaid negative pressure tank, said negative pressure tank being adaptedto admit the primary ozone water while a reduced pressure is establishedwithin the lumen of said degassing tube.
 16. The ozonization apparatusaccording to claim 15, wherein the degassing tube is made of afluororesin or a silicone resin.
 17. A photoresist stripping apparatuscomprising the ozonization apparatus according to claim 11.